Per the manufacturer's website:

Surface Primer is available in a range of basic shades most frequently employed to prepare the surface of the model or miniature before starting the painting process. Primers can be applied on all surfaces, resin, PVC, brass, white metal or wood. The primer preserves even the smallest detail of a model, and improves the adherence of the colors applied on this base. It is recommended to apply the Primer in various layers; the product dries rapidly and forms a homogeneous film of extraordinary strength and resistance within a few hours after application. Surface Primer can be used directly or diluted with Vallejo Airbrush Thinner or Flow Improver. The recommended compressor settings are around 15-20 PSI or 0.5 to 1 kg. For best maintenance of the airbrush, it is recommended to use the Vallejo Airbrush Cleaner.
Safety: Surface Primer is not flammable, and does not contain solvents. Please see also certified safety information of the product on the Safety page.
Packaging: Available in 17 ml./0.57 fl.oz. bottles (with eyedropper).